Setup Nightlies (#44741)

Summary:
This change adds a separate workflow for Nightlies. This workflow do not run tests on iOS and Android and proceed to release a nightly.

**🚨 Important 🚨** We need to update the GHA secrets as there is none set.

_Note: This is a first step to ensure that we can release Nightlies from GHA. I'll factor out all the actions in following updates to cleanup and refactor once we know that everything works!_

## Changelog:
[INTERNAL] - Add nightlies workflow on GHA

Pull Request resolved: https://github.com/facebook/react-native/pull/44741

Test Plan:
1. Add the `pull_request` trigger to see the workflow start
2. Monitored the workflow to make sure that it worked
3. Tested the nightly locally
4. Removed the `pull_request` trigger, otherwise we would publish a nightly on each PR! xD

Reviewed By: cortinico

Differential Revision: D58084002

Pulled By: cipolleschi

fbshipit-source-id: 593145392fe686930ccb00beb68d9130b8401cbc